An anti-rust technology has been widely used in the art, where a blast material consisting of a core substantially made of iron and a multi-layered particle aggregate substantially made of zinc and formed around the core is projected on the surface of a coated metal formed article to form a porous covering layer (hereinafter, which may be also referred to as a zinc-containing porous layer). Then, the zinc-containing porous coating layer is subjected to a chromate treatment to allow a coating layer made of a chrome compound such as chromic acid, dichromic acid, chromate, or the like to be impregnated into such a coating layer (see, Patent Document 1).
The anti-rust technology is carried out industrially on a large scale because a coated metal formed article can be allowed to show a high adhesion on the surfaces of a zinc-containing porous coating layer and a coated metal formed article and facilitated to have a uniform thickness of the coating layer, as well as being comparatively cheep in comparison.
Furthermore, a metal-surface treating agent that contains a nitrogen compound in a concentration of 0.1 g/l to 20 g/l and a zirconium compound in a concentration of 0.1 g/l to 50 g/l with respect to an aqueous resin solution in a concentration of 0.5 g/l to 200 g/l is disclosed (see, Patent Document 2).
Furthermore, a coated metal formed article, in which a porous coating layer made of zinc or a zinc-iron alloy, an intermediate layer made of a silicon compound/thermosetting resin, and a silicon compound layer provided as a surface synthetic resin layer are sequentially formed on the surface of a metal formed article, is disclosed (see, Patent Document 3).
Furthermore, there is disclosed a method for producing a corrosion-resistant iron material prepared by forming a porous coating layer made of zinc or aluminum on the surface of an iron formed article with a thermal-spraying device, and then forming a coating layer containing, for example, methyl silicate, ammonia silicate, pyrocatechine, trihydroxybenzoic acid ethyl ester, methyl trimethoxysilane, and tetrabutoxy zirconate by a heat treatment (see, Patent Document 4).    [Patent Document 1] JP 59-9312 B (Claims)    [Patent Document 2] JP 2000-204485 A (Claims)    [Patent Document 3] JP 2002-292792 A (Claims)    [Patent Document 4] JP 2003-328151 A (Claims)